This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. My laboratory is interested in structural aspects of cell-surface receptor/ligand interactions with relevance to human health and disease. We are engaged in expression and crystallization studies of numerous receptor extracellular domains both alone and in complex with their ligands. The receptor systems we study are primarily in the immune and nervous systems, with a special emphasis on understanding cross-reactivity in molecular recognition. Most of our projects are critically dependent on the ability to collect x-ray data at a synchrotron facility due to the generally small and moderate quality of the crystals which we can grow of large and heterogeneous protein complexes. In-house x-ray sources are not sufficient to measure useful data on most of our crystals, which are often few in number and extemely labor intensive to produce from the mammalian expression sources we utilize to make recombinant proteins.